Rechargeable lithium batteries are widely discussed in the literature and are readily commercially available. They typically consist of a positive electrode and a negative electrode spaced by a separator, an electrolyte, a case, and feedthrough pins respectively connected to the electrodes and extending externally of the case. Each electrode is typically formed of a metal substrate that is coated with a mixture of an active material, a binder, and a solvent. In a typical battery design, the electrodes comprise sheets which are rolled together, separated by separator sheets, and then placed in a prismatic case. Positive and/or negative feed through pins (i.e., terminals) are then connected to the respective electrodes and the case is sealed.
The negative electrode is typically formed of a copper substrate carrying graphite as the active material. The positive electrode is typically formed of an aluminum substrate carrying lithium cobalt dioxide as the active material. The electrolyte is most commonly a 1.1 mixture of EC:DEC in a 1.0 M salt of LiPF6. The separator is frequently a micro porous membrane made of a polyolephine, such as a combination of polyethylene and/or polypropylene which can, for example, be approximately 25 μm thick.
It is typical to use protection circuitry with lithium ion batteries to avoid potential deleterious effects. Thus, protection circuitry is frequently employed to terminate charging if the voltage or temperature of the battery (or any cell) exceeds a certain level. Moreover, it is common to incorporate a low voltage cutoff to disconnect the battery from its load if the voltage of the battery (or any cell) falls below a certain lower level. This latter precaution is taken to prevent permanent damage to the battery which can occur if a voltage greater than a Damage Potential Threshold (DPT) is applied to one of the electrodes. For example, corrosion or decomposition of the negative electrode substrate can occur if a voltage greater than a Substrate Dissolution Potential (SDP) is applied to the negative electrode.